The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased.
Different regions of a semiconductor wafer may have different pattern densities. These different pattern densities may lead to fabrication challenges. For example, during a polishing process, a dense region (i.e., higher density region) may be polished at a greater rate than an iso region (i.e., lower density region). Consequently, devices such as transistor gates in a dense region may have a significantly different height than transistor gates in an iso region, even though they should have similar heights. The gate height difference may result in device defects such as power shorting or high gate resistance.
Therefore, while existing semiconductor fabrication methods may have taken different pattern densities into account in some ways, they have not been entirely satisfactory in every aspect.